The present invention relates to a method and a device for maintaining or replacing a tether line anchoring a buoyancy unit to an underwater or seabed anchoring installation.
In this respect, reference is made to Japanese patent publication JP-57167887 and U.S. Pat. No. 6,457,908.
The upper termination part of a tether line is normally connected to the buoyancy unit by means of an upper interface component, while the lower tether termination part is connected to a lower interface component connected to a sea bed installation such as a sea bed anchor. The two interphase components, or also named coupling units, include well known hinge couplings performing a universal joint function when the buoyancy unit moves in the sea volume.
The area of application for the present invention is illustrated in the enclosed FIG. 1. A buoyancy unit 11, or pontoon unit, also named a mid water arch (MWA) is kept in position in the body of water 100 at a distance below the sea level/surface 24 by means of two tether lines 22a,22b. The upper part of each tether line is connected to the bottom of the pontoon 11, while the lower tether part is connected to an anchor structure 19A, 19B fixed to the sea bed surface 23. To save weight the lines in question is preferably made of synthetic fibers instead of steel wire rope.
In the example shown in FIG. 1, the buoyancy unit 11 is used to support or suspend a number of lines 120 that for example runs partly floating on their own, in smooth patterns from a sea bed installation in a hydrocarbon production plant (not shown) upwards through the body of water to a processing plant platform (not shown).